Drought, digging create greater risk of sinkholes

Drought and development-related excavation have created a higher likelihood of sinkholes for Washington County property owners, local experts said.

Retired farmer Tom Shaw said he has noticed the weather affects sinkholes on his 350-acre farm near the Washington County Agricultural Education Center. He has at least five sinkholes on his property, including one that is 20 feet wide. The sinkholes have been visible on the surface for at least 25 years, he said.

The sinkholes are surface depressions or openings in the ground created due to conditions such as underground erosion or the collapse of a cave or a mine.

Shaw fills the sinkholes on his property with rocks, but drought conditions or heavy rainfall can alter sinkholes, he said.

"When the weather is right, the rascal opens back up again," he said.

It takes millions of years for underlying rock formations to change, causing sinkholes. Construction projects can accelerate the process through digging and blasting work, which can change the hydrogeology, Joe Kraft, a soil scientist with U.S. Department of Agriculture's Natural Resources Conservation Service, said Thursday.

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More than 80 percent of Washington County - from Clear Spring to Smithsburg and Boonsboro - has karst topography that is prone to sinkholes, said Topper Sherwood, grant manager for the Hagerstown-based Western Maryland Resource Conservation and Development Council.

Karst is a limestone formation that is "as porous as Swiss cheese," Sherwood said.

"Sinkholes tend to occur in limestone karst regions, especially during drought," he said.

Drought raises the possibility of sinkholes by lowering the water table and emptying cavities in the karst, Sherwood said. The reduced pressure on the cavity walls can cause them to collapse, sometimes opening a sinkhole on the surface.

When it rains, water moving through the limestone increases the size of the cavity and the sinkhole, partially because of changing water pressure, he said.

The sinkholes can pose danger on farmland, roads and buildings, he said.

Additionally, sinkholes can affect water quality by introducing polluted surface water into underground aquifers, which can taint wells with pesticides and sewage, Sherwood said.

Some people don't think about the possibility of pollution and discard car batteries, dead animals and paint cans in sinkholes, said James Schlossnagle, district conservationist for the Natural Resources Conservation Service.

Most sinkholes in Washington County are about 3 to 5 feet wide and deep, Kraft said.

"We don't know exactly how many hundreds of sinkholes there are in Washington County - but it only takes one in the right place at the right time to cause major problems," Sherwood said.

The Western Maryland Resource Conservation and Development Council is creating a 20-page booklet to inform property owners about what sinkholes are and how they are formed, Sherwood said.

Officials with local Soil Conservation Districts and the National Resources Conservation Service are helping with the development of the booklet, which is partially funded by a $7,300 grant from the private Fish and Wildlife Foundation.

The booklet will focus on Washington, Frederick and Carroll counties, the three Maryland counties with the largest concentration of karst, Sherwood said.

When the booklet is finished in about eight months, there will be a few thousand copies printed and available at conservation district offices, Sherwood said. The booklet may also be posted on the Internet.

The booklet will contains maps, pictures and other information about sinkholes, he said.

If you come across a sinkhole, Sherwood suggests calling Schlossnagle at 301-797-6821, extension 121.

While there is a procedure for dealing with sinkholes, each case is slightly different and he prefers to see the sinkhole before making a recommendation, Schlossnagle said.